Vapor deposition apparatuses, i.e., ion-assisted vapor deposition apparatuses, have been conventionally known, each configured to irradiate ions onto a vapor deposition layer deposited on a substrate by vaporizing a thin-film material toward a surface of the substrate within a vacuum vessel, thereby densifying the vapor deposition layer. In each of such vapor deposition apparatuses, an ion beam(s) (gas ions) of relatively low energy is/are irradiated onto a substance body (or substance bodies) by an ion source(s), and neutralizing electrons (electrons) are irradiated onto the substance body (or substance bodies) by a neutralizing device called a neutralizer. This configuration enables the fabrication of a dense optical thin-film by virtue of a kinetic energy of the ion beam, while neutralizing an electric charge accumulated on the substrate(s) by the ion beam (see Patent Document 1, for example).
According to a technique described in the Patent Document 1, and as shown in FIG. 7 of the present application, an optical thin-film comprising a multi-layer film is obtained by alternately vaporizing a high refractive index substance and a low refractive index substance from a vapor deposition source 134 and alternately stacking them. Upon formation of films of the high refractive index substance and low refractive index substance, the substances once vaporized and attached onto substrates 114 are densified by argon ions and oxygen ions irradiated from an ion source 138, and charging of the substrates 114, a substrate holder, and the like is prevented by virtue of neutralizing electrons irradiated from a neutralizer 140.
Disclosed in the technique shown in the Patent Document 1 is a vapor deposition apparatus having a configuration where the vapor deposition source 134 and the ion source 138 are arranged at positions opposed to the substrates 114, i.e., at a bottom surface side of a vacuum vessel. In this apparatus, the distance between the vapor deposition source 134 and the substrate holder (substrates 114) is required to be kept at a constant ratio relative to a size of the substrate holder, so as to keep a film thickness distribution constant. As such, in case that the vapor deposition source 134 is arranged at an appropriate distance from substrates 114 in a vapor deposition apparatus provided with a substrate holder having a greater diameter, the apparatus is brought into an arrangement where the substrate holder is undesirably distanced from the ion source 138, thereby possibly deteriorating the effect of ion assistance.
To solve such a problem, techniques have been proposed (see Patent Documents 2 to 4), each configured to enhance an ion assistance effect by mounting an ion source at a side surface position of a vacuum vessel which position is closer to a substrate holder than a vapor deposition source, thereby avoiding deterioration of film-formation efficiency.    Patent Document 1: Japanese Patent Laid-Open No. 2007-248828A    Patent Document 2: Japanese Patent Laid-Open No. 2000-129421A    Patent Document 3: Japanese Patent Laid-Open No. 2004-131783A    Patent Document 4: Japanese Patent Laid-Open No. 2006-045632A
According to the techniques disclosed in the Patent Documents 2 to 4, the ion source is mounted at a position closer to the substrate holder than the vapor deposition source, or at a position which is closer to the substrate holder than the vapor deposition source and which is near a side surface of the vacuum vessel, thereby preventing deterioration of an effect of ion assistance, and deterioration of a film-formation efficiency by ion plating, to a certain extent. More specifically, according to the techniques described in the Patent Documents 2 to 4, ion beams irradiated from ion sources can be irradiated onto substrates while keeping higher energy states of the ion beams. However, it has been desired to obtain a higher effect of ion assistance.
Meanwhile, examples of optical thin-films to be obtained by combining a high refractive index substance with a low refractive index substance include a cut filter for cutting off a light at a particular wavelength and for transmitting light at wavelengths other than the particular wavelength through the filter. In case of optical thin-films like the cut filter, those films, which have less loss of transmitted light and less white cloudiness, are regarded as more excellent ones, respectively, and a value (%) of a sum of a reflectance and a transmission is adopted as an index of quality of such a film. Further, it is typically assumed that thin films having such a value closer to 100% are more excellent optical thin-films. It has been thus desired to obtain an apparatus for forming an optical thin-film, having a value of a sum of a reflectance and a transmission which is closer to 100%, while maintaining a higher film-formation efficiency as mentioned above.
However, in case of the technique disclosed in the Patent Document 2, the substrate holder is made planar, so that the ion assistance effect to be obtained by the ion source provided at a lateral side of the vacuum vessel is not likely to be kept constant relative to substrates, thereby causing a problem that a film-quality of an optical thin-film to be resultingly obtained is not likely to be kept homogeneous. In turn, although the substrate holders of the Patent Documents 3 and 4 are dome-shaped, no disclosures are found therein about positional relationships between the ion source(s) and the substrate holder, such as an angle of ion beams to be irradiated from the ion sources onto placed substrates. Thus, although the ion assistance effect may be obtained by the techniques disclosed in the Patent Documents 3 and 4, the extent of ion assistance effect related to a mounting position of the ion source(s) is not shown in these documents. It has been thus difficult in the conventional techniques to obtain an optical thin-film having superior optical characteristics with a homogeneous film-quality, while obtaining a higher ion assistance effect.
It is therefore desired to provide an optical thin-film vapor deposition apparatus comprising an ion source, which apparatus allows for obtaining a higher ion assistance effect and obtaining an optical thin-film having a homogeneous film-quality and excellent optical characteristics. It is also desired to provide: an optical thin-film vapor deposition apparatus capable of producing a high-performance optical thin-film while achieving reduction of a production cost of the optical thin-film; and a production method of an optical thin-film having a higher performance with a lower production cost.